Composite Conducts Heat to Remove Salt From Seawater

Desalination attempts for converting seawater to fresh, drinkable water are on the rise. The decision to pursue or not pursue desalination projects is a ballot item right now in Santa Cruz, Calif., the city nearest to the town I live in. It's a pressing issue in many parts of the world, including here where the aquifer has been shrinking for a couple of decades.

A new composite material invented by researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) may help bring down the cost of some desalination plants. These processing plants require highly specialized, expensive infrastructure, including pipelines made of titanium and various forms of high-alloy steel that resist the corrosive action of salt water. Although pipeline cost isn't the only expense, expense in general is one of the objections to desalination.

A new composite material for saltwater desalination plant pipelines may help bring down the cost of the process. (Source: Fraunhofer IFAM)

The most common desalination method is multi-stage flash distillation, a form of thermal distillation. In thermal distillation desalination methods, the pipes must also be heat-resistant, since this process requires them to be heated until water sprayed on them boils and evaporates, leaving behind salt and chemical residues. Pipes in desalination plants must therefore be highly durable, corrosion-resistant, heat-resistant, and long-lasting. They must also have a surface that can be easily coated with seawater, so the fresh water evaporates correctly.

The Fraunhofer IFAM's polymer composite conducts heat and can be produced in continuous lengths, which the researchers say will make it less expensive than the specialty metals it can replace. Although a plastic, the composite conducts heat because it contains copper microfibers, about 50 percent by volume. "This does not change the processing properties of the composite, and it can still be processed as any other polymer would," said Arne Haberkorn, an IFAM scientist, in a press release.

The material has been developed, and the researchers exhibited it at the Composites Europe 2012 trade show in Dusseldorf, Germany, October 9 to 11. Their next step is to optimize its thermal conductivity by testing it in a pilot seawater desalination plant.

During testing, they expect to measure the composite's thermal conductivity, observe how much microorganism-based coating forms on the pipes, and see to what extent the pipes corrode in a salty environment. In the pilot plant's evaporation process, hot gas heated to 70C will run through the pipelines. This temperature is lower than some of the highest temperatures in multi-stage flash distillation, which can run up to 120C. The benefit of lower temperatures is that the material doesn't corrode as quickly, there's less deposit buildup on the pipes, and the inside and outside pressure differential is much less. This results in pipes that last longer and a process that requires less maintenance.

I'd like to see technology implemented as soon as possible. But I don't have a lot of faith in our current economic model. I struggle to support continual government funding to in some cases force development in an area that might not be viable.

jmiller, personally I'd rather see technology get implemented sooner rather than later for several reasons: makes more people aware of it, gets accepted faster, and helps bring down costs sooner, among them. Government tax breaks can help all these happen. At least using our current economic model, it's higher volumes in manufacturing that can help to make things more affordable.

jmiller, thanks for the comment--I enjoy reporting and writing articles that showcase engineers who've designed something with innovation and ingenuity, which can make major improvements in our lives, too.

I haven't read anything definitive about why the strawberries aren't as tasty or nutritious. But just taking the salt out doesn't turn seawater into freshwater. It may be drinkable but it's not the same.

Maybe a Gadget Freak will come up with something for grey water or capturing rain water for the lawn.

Ann, RO water purifications are commonly implemented with house hold water purifiers. It's a five stage purification method and so far I had not seen it with any large scale implementation. If my knowledge is right, Arab countries are implemented multi stage flash distillation method, where water is heating and reheating multiple times. Now there are some new technologies like osmosis technologies (Reverse, Forward), Electro dialysis and Distillation methods like Thermal Distillation, Multi-Effect distillation etc are implemented in certain countries.

I do agree with the idea of tax breaks to encourage developement of technologies that make things better or cheaper. But I struggle with tax breaks for homeowners just to put in the solutions. I'd rather see the government spending money to make things more affordable, rather than giving us money to use products that aren't financially viable right now.

I do agree there are areas we shouldn't be. However, it's interesting how many people choose to live there. In the case of a lot of cities, more and more people are living in a n area that just can't support the population. In the case of some cities, we have literally built in areas below sea level. In the end, sometimes, I think every time we build a solution to a problem. The world finds a way to build a bigger idiot.

So why aren't the strawberries as good. Is the water quality not as good? Did some of the salt not get our of the water? I agree with the idea of using grey water because that would be available in a lot more of the middle United States. But I'm also curious with some of the problems being experienced with current systems.

I think often problems like this are solved by going through a set of steps where the technology to solve the problem is solved and then economics come in and are improved and then the technology to solve the problem is improved and then the economics come in. It's a cycle of improvement that ends up developing a final solution. It's fun for me to watch because it just shows the never give up attitude of engineers.

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